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PySnooper: Never use print for debugging again

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Re: PySnooper: Never use print for debugging again

#121

Post by [deleted] »

Gibbon1 wrote: post #91
rossdavidh wrote: post #65

While I sometimes use one debug tool or another, I have never understood the aversion to print statements reflected in the title. Sometimes, often even, a print statement is just fine, and anything else is overabstracting it. Not saying other options aren't nice to have available, just that there is nothing wrong with using a simple print statement in many situations.

Because the observability you get with a print statement is limited. You can't do further investigation without modifying the code and running it again. With a debugger you can explore the program state interactively. My experience with python is limited but in my day job it's not uncommon to be tracking down stuff that happens infrequently. Debug cycles get brutally long.

[deleted]

Re: PySnooper: Never use print for debugging again

#122

Post by spc476 »

badatshipping wrote: post #83

This is a thoughtful hack but the real solution here is a) make debuggers easier to set up and b) make your project easily debuggable with a debugger from the beginning. Like, debugging should be considered part of programming, and a local dev environment that can’t be debugged should be viewed to be as broken as a codebase without e.g. a way to run the server in watch mode. Also someone should make a debugger that s…

Until such a day comes, `printf()` debugging will still be useful. Heck, even after that day comes, it may still find uses.

The other day I was writing LPEG [1]. I had a rule that wasn't firing for some reason and I wanted to know why LPEG was skipping that part of the input. It was not a simple matter to fire up a debugger and put a breakpoint on the rule:

    -- look for 1 or more ASCII characters minus the colon
    local hdr_name = (R"\0\127" - P":")^1 -- [2]
I mean, I could put a breakpoint there, but that would trigger when the expression is being compiled, not run. LPEG has its own VM geared for parsing (it really is its own language) so yes, it is sometimes difficult to debug (especially when you end up with a large parsing expression to parse a document---I only found the bug when I was creating another document similar to my initial testing document that was just different enough).

Fortunately, there is a way to hook into the parsing done by LPEG and I was able to insert literal print statements during parsing that showed what exactly was going on (my rule was a bit too promiscuous).

[1] Lua Parsing Expression Grammar http://www.inf.puc-rio.br/~roberto/lpeg/

[2] Yes, a regular expression for that is smaller than what I typed, but with LPEG, I can reuse that rule in other expressions. Also, that wasn't the actual rule used, but the effective rule I was using.

Re: PySnooper: Never use print for debugging again

#125

Post by nijave »

badatshipping wrote: post #83

This is a thoughtful hack but the real solution here is a) make debuggers easier to set up and b) make your project easily debuggable with a debugger from the beginning. Like, debugging should be considered part of programming, and a local dev environment that can’t be debugged should be viewed to be as broken as a codebase without e.g. a way to run the server in watch mode. Also someone should make a debugger that s…

Or just use a logger with proper log levels

Re: PySnooper: Never use print for debugging again

#126

Post by TazeTSchnitzel »

Xavdidtheshadow wrote: post #119
iamgopal wrote: post #51

Earlier quoted context omitted.

This is what I'm going to try to use in every language from now on.

Except for JS, which will execute `1/0` happily and without complaint. For that, I usually do `undefined.foo`.

JS has a debugger keyword!

Re: PySnooper: Never use print for debugging again

#127

Post by joshmarlow »

yason wrote: post #75

Happy to see new tools for debugging. Yet it's the good old print that I most often end up using. Debugging is very context-sensitive: adding prints makes sense because I know exactly what I'm interested in, and I can drill down on that without being disturbed by anything else. I can print low-level stuff or high-level indicators, depending where my debugging takes me. There's no ready-made recipe for that. Some code…

Assuming you use Python, you might like this library - https://github.com/robdmc/behold

It gives you contextual debugging - so you can put fancy prints throughout a function but they are silent unless some context is true. It's useful for when you have a hot path that is executed a lot but you only want debug prints for one of those invocations.

Re: PySnooper: Never use print for debugging again

#128

Post by anitil »

yason wrote: post #75

Happy to see new tools for debugging. Yet it's the good old print that I most often end up using. Debugging is very context-sensitive: adding prints makes sense because I know exactly what I'm interested in, and I can drill down on that without being disturbed by anything else. I can print low-level stuff or high-level indicators, depending where my debugging takes me. There's no ready-made recipe for that. Some code…

I've definitely had the experience of using custom_logger.log("something"), then checking the system log. Nope, no there, must be in /var/log/app ... nope. Hmm oh I know! I'll turn up the logging in the config file, wherever that is. Still nothing. Did I need to compile in some flag?

Screw it. print, run directly from shell, done.

Re: PySnooper: Never use print for debugging again

#129

Post by thatoneuser »

anitil wrote: post #128
yason wrote: post #75

Happy to see new tools for debugging. Yet it's the good old print that I most often end up using. Debugging is very context-sensitive: adding prints makes sense because I know exactly what I'm interested in, and I can drill down on that without being disturbed by anything else. I can print low-level stuff or high-level indicators, depending where my debugging takes me. There's no ready-made recipe for that. Some code…

I've definitely had the experience of using custom_logger.log("something"), then checking the system log. Nope, no there, must be in /var/log/app ... nope. Hmm oh I know! I'll turn up the logging in the config file, wherever that is. Still nothing. Did I need to compile in some flag? Screw it. print, run directly from shell, done.

Fuck var/log/app.

Re: PySnooper: Never use print for debugging again

#130

Post by thatoneuser »

yason wrote: post #75

Happy to see new tools for debugging. Yet it's the good old print that I most often end up using. Debugging is very context-sensitive: adding prints makes sense because I know exactly what I'm interested in, and I can drill down on that without being disturbed by anything else. I can print low-level stuff or high-level indicators, depending where my debugging takes me. There's no ready-made recipe for that. Some code…

I pretty exclusively rely on prints and intuition. Honestly I've implemented logging frameworks in different production situations and never gotten use out of them. Like you say - they don't answer the questions you need answered.
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